> -----Original Message----- > From: Yishai Hadas [mailto:yishaih@xxxxxxxxxx] > Sent: 01 December 2022 15:29 > To: alex.williamson@xxxxxxxxxx; jgg@xxxxxxxxxx > Cc: kvm@xxxxxxxxxxxxxxx; kevin.tian@xxxxxxxxx; joao.m.martins@xxxxxxxxxx; > leonro@xxxxxxxxxx; shayd@xxxxxxxxxx; yishaih@xxxxxxxxxx; > maorg@xxxxxxxxxx; avihaih@xxxxxxxxxx; cohuck@xxxxxxxxxx > Subject: [PATCH V2 vfio 02/14] vfio: Extend the device migration protocol > with PRE_COPY [...] > +/** > + * VFIO_MIG_GET_PRECOPY_INFO - _IO(VFIO_TYPE, VFIO_BASE + 21) > + * > + * This ioctl is used on the migration data FD in the precopy phase of the > + * migration data transfer. It returns an estimate of the current data sizes > + * remaining to be transferred. It allows the user to judge when it is > + * appropriate to leave PRE_COPY for STOP_COPY. > + * > + * This ioctl is valid only in PRE_COPY states and kernel driver should > + * return -EINVAL from any other migration state. > + * > + * The vfio_precopy_info data structure returned by this ioctl provides > + * estimates of data available from the device during the PRE_COPY states. > + * This estimate is split into two categories, initial_bytes and > + * dirty_bytes. > + * > + * The initial_bytes field indicates the amount of initial precopy > + * data available from the device. This field should have a non-zero initial > + * value and decrease as migration data is read from the device. > + * It is recommended to leave PRE_COPY for STOP_COPY only after this field > + * reaches zero. Leaving PRE_COPY earlier might make things slower. > + * > + * The dirty_bytes field tracks device state changes relative to data > + * previously retrieved. This field starts at zero and may increase as > + * the internal device state is modified or decrease as that modified > + * state is read from the device. > + * > + * Userspace may use the combination of these fields to estimate the > + * potential data size available during the PRE_COPY phases, as well as > + * trends relative to the rate the device is dirtying its internal > + * state, but these fields are not required to have any bearing relative > + * to the data size available during the STOP_COPY phase. > + * > + * Drivers have a lot of flexibility in when and what they transfer during the > + * PRE_COPY phase, and how they report this from > VFIO_MIG_GET_PRECOPY_INFO. > + * > + * During pre-copy the migration data FD has a temporary "end of stream" > that is > + * reached when both initial_bytes and dirty_byte are zero. For instance, > this > + * may indicate that the device is idle and not currently dirtying any internal > + * state. When read() is done on this temporary end of stream the kernel > driver > + * should return ENOMSG from read(). Userspace can wait for more data > (which may > + * never come) by using poll. > + * > + * Once in STOP_COPY the migration data FD has a permanent end of > stream > + * signaled in the usual way by read() always returning 0 and poll always > + * returning readable. ENOMSG may not be returned in STOP_COPY. > Support > + * for this ioctl is optional. Isn't mandatory if the driver claims support for VFIO_MIGRATION_PRE_COPY? Other than that looks fine to me. Reviewed-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
